Continuous shroud structure



F 6, 1968 P. D. SAUNDERS 3,367,630

CONTINUOUS SHROUD STRUCTURE Filed Jan. 16, 1967 WITNESSES INVENTOR /taw 471% Paul D. Sounders United States Patent 3,367,630 CONTINUOUS SHROUD STRUCTURE Paul D. Saunders, Montain View, Calif., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania- Filed Jan. 16, 1967, Ser. No. 609,477 8 Claims. (Cl; 253-77) ABSTRACT THE DISCLOSURE The invention provides a shrouded turbine rotor blade structure comprising two circular half shroud sections having circular grooves therein, within which the blade tenons are received, the half sections being secured to each other by securing means, such as units extending between the blades. The shroud half sections are formed by a plurality of arcuate segments disposed in staggered or overlapping relation with each other to provide a continuous unitary shroud of 360 circumferential extent.

This invention relates, generally, to elastic fluid axial flow apparatus and, more particularly, to shrouds for blades utilized in such apparatus, such as turbines.

The advantages of providing shrouding on the tips of compressor and turbine rotor blades are well known. However, the provision of a satisfactory shroud structure involves certain difficulties, particularly in the case of marine turbines which operate at variable speeds.

An object of this invention is to provide a continuous shroud for joining rotor blades over 360.

Another object of the invention is to eliminate thermal bending stresses in the end blades of groups of blades joined by shroud segments.

A further object of the invention is to provide friction damping at the ends of the blades to attenuate vibrations at lower turbine speeds.

Still another object of the invention is to substantially eliminate centrifugal stresses on blade tenon rivets.

A still further object of the invention is to provide better shroud sealing by eliminating gaps in the shroud.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art.

In accordance with one embodiment of the invention, the shroud structure for a transverse row of turbine blades comprises two annular half shroud sections held on T- shaped tenons on the outer ends of the blades by rivets extending axially through the two sections. The inner face of each section is grooved to receive arms of the T- shaped tenons. Thus, the tenons carry the centrifugal forces on the shroud and provide surfaces for frictional damping at lower turbine speeds. At higher speeds, the centrifugal forces lock all the blade tips together into one continuous ring. The rivets have no centrifugal operating stresses on them. Provision is made for thermal expansion of the shroud by staggered cuts in the two half shroud sections.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanyin g drawing, in which:

FIGURE 1 is a view, in elevation, of a portion of a turbine rotor having a shroud constructed in accordance with the present invention;

FIG. 2 is a view, partly in elevation and partly in section. taken along the line II-1'I in FIG. 1;

FIG. 3 is an exploded view, in perspective, of a portion of the rotor and shroud structure; and

FIG. 4 is a reduced view, in perspective, of the two half shroud sections.

Referring to the drawing, and particularly to FIG. 1,

3,367,630 Patented Feb. 6, 1968 the structure shown therein includes a portion of a rotor core 10', a transverse annular row of blades 11 and an annular shroud 12 surrounding the outer ends or tips of the blades 11 which may be of the usual airfoil contour. The blades 11 may be attached to the rotor core 10 by means of root portions 13 disposed in a suitable groove in the core. The blades extend radially outwardly with respect to the longitudinal axis of the rotor and they may constitute one stage of a multi-stage axial flow turbine.

In order to provide a continuous shroud which joins all of the blades 11 over 360, the shroud 12 comprises two annular half sections 14 and 15 which are held together by rivets 16 extending transversely thereof and preferably parallel to the axis of the rotor. As shown in FIG. 3, the rivets 16 are disposed between the blades 11 and do not interfere with the blades. The inner face of the half section 14 has a groove 17 therein having a side 18 which frictionally engages the under side of an arm 19' of a T-shaped tenon 20 on the outer end of each blade 11. Likewise, the half section 15' has a groove 21 therein having a side 22 which frictionally engages an arm 23 of each T-shaped tenon 20.

Thus, the tenons, which are integral with the blades, and the sides 18 and 22, which are integral with the half sections 14 and 15, respectively, carry the centrifugal forces of the shroud and provide surfaces for frictional damping at lower turbine speeds. At higher speeds, the centrifugal forces lock all the blade tips together into one continuous ring. The rivets 16 have no centrifugal operating stresses on themand serve only to retain the two shroud half sections 14 and 15 together. It may be possible to utilize a fewer number of rivets than is indicated on the drawing.

In order to provide for thermal expansion of the shroud, radial cuts 24 are made in the shroud half sections to divide them into preferably equal arcuate segments as shown in FIG. 4. The cuts 24 are so staggered that the segments of one half section overlap the segments of the other half section. Since the shroud is not directly attached to the blades, bending stresses in the end blades of a group caused by thermal growth of the shroud are eliminated. Also, better sealing by the shroud is obtained since the cuts 24 are staggered and there are no gaps directly through the shroud. As shown in FIG. 2, the outer portions of the half sections 14 and 15 have faces which abut at 25, thereby closing the gaps between the ends of the blades 11.

As explained hereinbefore, there are no centrifugal stresses on the rivets 16 which hold the two shroud half sections 14 and 15 together. In prior shroud structures centrifugal stresses on blade tenon rivets have resulted in failures. This potential failure area is eliminated in the present structure.

The present structure also precludes high vibratory stresses which have caused failures in the past. The elimination of vibratory build up provides a much greater speed range for existing blade designs.

Furthermore, existing blade designs may be utilized in the present structure by modifying the blade tenons only. The blades and the shroud may be readily assembled as no pitch measuring, no heat treating, no tenon riveting is required.

The blades can be re-used after having been removed from the rotor. The blading may be removed, repaired or replaced without scrapping good blades. Field assembly problems are reduced by eliminating punching tenon holes, pitch measuring and welding.

In view of the foregoing advantages it is apparent that the continuous shroud structure provided by this invention is an improvement over prior structures. Furthermore, the present structure may be readily manufactured and economically installed.

Since numerous changes may be made in the above-described construction, and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In elastic fluid utilizing apparatus, a rotor having a transverse row of blades, a shroud surrounding the outer ends of the blades, said shroud comprising two annular half sections, means extending through the sections to hold them together, projecting means on each blade, and annular means on each half section engaging said projecting means to retain the shroud in position on the blades, said annular half sections having staggered cuts therein.

2. The structure defined in claim 1 wherein said annular means is integral with each half section.

3. The structure defined in claim 1 wherein said annular means is disposed on the inner faces of the half sections of the shroud.

4. The structure defined in claim 1 wherein the projecting means is generally of a T-shape.

5. The structure defined in claim 4 wherein the annular means is a groove having sides engaging arms of the T-shaped means.

6. The structure defined in claim 1 wherein the annular half sections have mutually abutting faces.

7. The structure defined in claim 1 wherein the annular half sections comprise equal arcuate segments with the segments of one half section overlapping the segments of the other half section.

8. The structure defined in claim 1 wherein the annular means and the projecting means have frictionally engaging surfaces.

References Cited UNITED STATES PATENTS 1,010,750 12/1911 Green 253-77 1,720,754 7/1929 Baurnann 25377 FOREIGN PATENTS 461,307 6/1928 Germany.

EVERETTE A. POWELL, JR., Primary Examiner. 

